Natural oils and their derivatives continue to become increasingly important as alternatives to dwindling supplies of petroleum and also because of the environmental concerns over petroleum based chemical feedstocks. Natural oils such as soybean oil, corn oil, linseed oil etc. have already been utilized as feedstocks for the development of thermoset and thermoplastic materials, fuels, cosmetic ingredients, and many other applications. Gels of petroleum derived hydrocarbons find utility in a number of important industrial applications such as fracturing fluids and viscosifers in the oil field industry. They also find utility as carriers or vehicles in the ink industry and as thickeners in paints and coatings. In addition they have wide utility in the personal care and cosmetic industry. Hydrocarbon gels have traditionally been made by one of two methods. In one method an organometallic gellant, most commonly an aluminum acylate, or other aluminum compound is added to the hydrocarbon with heating in order to solubilize the gellant in the liquid hydrocarbon. Gelation presumably takes place by a mechanism in which the organoaluminum compound forms long polymer chains or aggregates in the hydrocarbon. Another method involves the addition of a thermoplastic resin such as a block copolymer or a polyamide resin to the hydrocarbon with heating in order to dissolve the polymer in the liquid hydrocarbon. Gellation in these systems presumably takes place by either physical crosslinking or chemical crosslinking via hydrogen bonding. To date, these traditional methods used to viscosity or gel petroleum based hydrocarbons have not been successfully applied to natural oils, and thus these natural oil gels have not been widely available as alternatives to hydrocarbon gels.
The primary means for increasing the viscosity or gelation of natural oils has historically been referred to as “heat-bodying” the oil. In this process, unsaturated natural oils are subjected to high temperatures typically 300-340 deg C. in an inert atmosphere in order to promote chemical crosslinking at the sites of unsaturation in the triglyceride oil. This process as described in U.S. Pat. No. 5,122,188 typically results in oils with viscosities in the range 1600-1800 centipoise. In order to obtain higher viscosities, a second type of heat-bodying process is employed in which the high temperature heating is continued until the oil is irreversibly gelled. This intractable gel is then heated at about 340 deg C. with unmodified oil to produce the desired viscosity. It is often necessary to filter insoluble clumps of gelled oil from these blends. In addition, because both of these processes result in irreversible chemical crosslinks between the triglyceride oil chains, it is difficult to maintain precise control of the viscosity. Both of these processes also require rigorous exclusion of oxygen in order to prevent oil degradation and discoloration. It is also not possible to provide hard gels which are thermoreversible by this process.
More recently it has been reported that natural oils have been successfully gelled by using high molecular weight block copolymers that are specifically designed to be compatible with the natural oils. U.S. Pat. No. 7,674,848B2 and U.S. Pat. No. 7,625,967B2 both disclose the gelation of natural oils by combining block copolymers incorporated at various levels into the oil, and then applying heat and shear in order to obtain a homogenous gel. However, there are several disadvantages to this method. The block copolymers used must be specifically designed for compatibility with the particular oil used (apparently one copolymer is not compatible with a broad range of oils); gels of low viscosity are obtained, relative to gels provided by the present invention, even at high loadings (20%) of the block copolymers. Apparently hard clear gels or clear gels that exhibit no flow or tackiness at ambient temperature are difficult to obtain even with high loadings of block copolymer; viscosity is controlled by the styrene content of the block copolymer, requiring a range of different gellants. It should also be recognized that these “natural oil gels” are essentially blends of natural oils with up to 50% loadings of synthetic block copolymers thus reducing the attractiveness of this method from an environmental standpoint.